Fixed variable hybrid system

ABSTRACT

A fixed/variable hybrid system has modified constant flow open center hydraulic valves (“fixed/variable valves”), including an open center core, spools, a power core, and a tank galley. A small fixed displacement pump provides fluid at a constant rate to the open center core. A variable displacement piston pump provides fluid directly to the power core as needed. Activation of spools partially restricts the open center core causing an increase in fluid pressure that is communicated to the variable displacement piston pump&#39;s load sense signal port, causing the pump to increase fluid flow and pressure to the power core. Activated spools direct pressurized fluid from the power core to the applications through selected hydraulic ports. Activated spools also direct fluid flow from selected hydraulic ports via the tank galley to a hydraulic tank. Pumping the majority of fluid only on an as-needed basis results in significant efficiencies.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation for co-pending U.S. application Ser.No. 13/385,946, filed Mar. 15, 2013, which is a continuation of U.S.application Ser. No. 12/220,331, filed Jul. 23, 2008, which, in turn,claims the benefit of and priority from U.S. provisional applicationSer. No. 60/951,560, filed Jul. 24, 2007, all of the disclosures ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to hydraulic valve systems used, forexample, in off-road earth moving, construction, and forestry equipment,such as backhoes, log loaders, feller bunchers, wheel loaders, and thelike. Hydraulic valve systems are utilized, for example, to causepistons to move a boom or bucket loader in a backhoe. The presentinvention relates to an improved design for such hydraulic valvesystems.

2. Brief Description of the Related Art

Prior art hydraulic valve systems include the open center hydraulicvalve system 110 illustrated in FIG. 1. The open center hydraulic valvesystem 110 in FIG. 1 is illustrated in a hydraulic circuit diagram inschematic form as would be understood by a skilled practitioner. Theopen center hydraulic valve system 110 of FIG. 1 presently is in commonuse, for example, in off-road earth moving, construction, and forestryequipment.

While variations in the basic design of such a prior art open centerhydraulic valve system 110 exist, the fundamental components andoperation of such a system are briefly described below.

The prior art open center hydraulic valve system 110 of FIG. 1 typicallyincludes a hydraulic fluid tank 112, one or more constant flow opencenter hydraulic valve banks (“valves”) 114, and a fixed displacementpump 116. Each valve 114, in turn, may include one or more spools 118,with each spool 118 being activated by a spool actuator 120. The spoolactuators 120 may be activated by an equipment operator using a numberof known means (not illustrated), such as mechanically (for example,using a lever), electrically (for example, using a solenoid receiving anelectrical signal from a switch, a joystick, a computer, or othermeans), hydraulically, pneumatically, or otherwise.

In order to illustrate the operation of a spool 118 to selectivelyinterconnect hydraulic pathways within a valve, a simplified set ofdrawings illustrating how a spool 118 of a simple prior art constantflow open center (“CFO”) valve 136 is capable of redirecting theconstant flow of hydraulic fluid is provided in FIGS. 2A, 2B, and 2C.There, spool 118 is capable of providing selective hydrauliccommunication with either of a pair of hydraulic ports 122 and 124,depending upon the position of spool 118. The hydraulic ports 122 and124 are hydraulically connected to a cylinder 126 on either side of apiston 128. The simple CFO valve 136 has a number of internal hydraulicpathways which permit the spool 118, depending on its position, todirect hydraulic fluid flow to or from hydraulic ports 122 and 124.

For example, in FIG. 2A, the spool 118 is in the neutral position. Inthat position, fixed displacement pump 116 pumps hydraulic fluid at aconstant rate through open center core 130. The spool 118 does notobstruct or restrict the hydraulic fluid flow through the open centercore 130, which proceeds to the tank galley 132, and then through tankgalley 132 to hydraulic fluid tank 112. The spool 118 in the neutralposition blocks the flow of hydraulic fluid to or from hydraulic ports122 and 124, on the one hand, and either the open center core 130 or thetank galley 132, on the other hand. The result is that no net hydraulicfluid flows into or out of cylinder 126 either above or below piston128. The piston 128 and associated load 134 do not raise or lower.

In FIG. 2B, on the other hand, spool 118 is caused to move to a firstnon-neutral position (upward) where spool 118 partially restricts thehydraulic fluid flow provided by fixed displacement pump 116 throughopen center core 130, raising the hydraulic pressure of the hydraulicfluid upstream of the spool 118 (i.e., between the spool 118 and thefixed displacement pump 116). The spool 118 also opens a hydraulicpathway within the simple CFO valve 136 for net hydraulic fluid to flowfrom the open center core 130 through hydraulic port 122 into thecylinder 126 below the piston 128. At the same time, spool 118 opens ahydraulic pathway in simple CFO valve 136 between hydraulic port 124 andthe tank galley 132 allowing net hydraulic fluid to flow out of thecylinder 126 above the piston 128 to the tank galley 132 and tohydraulic fluid tank 132. The result is that there is net hydraulicfluid flow into the cylinder 126 below the piston 128 and out of thecylinder 126 above the piston 128; thus, the piston 128 and itsassociated load 134 is caused to rise.

Further, in FIG. 2C, spool 118 is caused to move to a second non-neutralposition (downward), causing spool 118 to partially restrict thehydraulic fluid flow provided by fixed displacement pump 116 throughopen center core 130, raising the hydraulic pressure upstream of thespool 118. The spool 118 opens a hydraulic pathway within the simple CFOvalve 136 permitting net hydraulic fluid flow from the open center core130 through hydraulic port 124 into the cylinder 126 above the piston128, while at the same time opening a hydraulic pathway betweenhydraulic port 122 and tank galley 132 allowing net hydraulic fluid toflow out of the cylinder 126 below the piston 128. The result is thatthe piston 128 and its associated load 134 is lowered.

The operation of the spool 118 in the prior art open center hydraulicvalve system 110 is similar to the operation of the spool 118 in theprior art simple CFO valve 136 described above; however, as illustratedand disclosed in the schematic diagram of FIG. 1, the fluid pathwayswithin prior art open center hydraulic valve system 110 that areselectively interconnected by spool 118 differ to a certain extent.

Referring once again to the prior art open center hydraulic valve system110 illustrated in FIG. 1, each spool 118 is capable of selectivehydraulic communication with a pair of associated hydraulic ports 122and 124. Each pair of hydraulic ports 122 and 124, in turn, maycommunicate hydraulically with equipment applications (such as a boom ona backhoe) in which the open center hydraulic valve system 110 is usedto operate, typically utilizing a cylinder and a piston. The hydraulicports selectively provide pressurized hydraulic flow to or from thecylinder on either side of the piston.

Referring again to FIG. 1, each spool 118 of each valve 114, and, hence,each pair of hydraulic ports 122 and 124 associated with each spool 118,is associated with a function of the application on the equipment withinwhich the open center hydraulic valve system 110 is utilized. In theexample illustrated in FIG. 1, one of the spools 118 (and the associatedpair of ports 122 and 124) is associated with the each of the followingfunctions, which can be found, for example, in a backhoe: boom, bucket,stick, swing, stabilizer, boom loader, bucket loader, and auxiliary.Those functions are chosen for purposes of illustration, and, as wouldbe recognized by skilled practitioners, those functions can vary,depending on the equipment and applications to which the open centerhydraulic valve system 110 is assigned.

The valves 114 include several hydraulic fluid pathways that may beselectively interconnected by activation of the spool 118, including anopen center core 130, a power core 138, and a tank galley 132. The fixeddisplacement pump 116 pumps hydraulic fluid (at a constant flow rate fora given engine speed) from the hydraulic fluid tank 112 into the opencenter core 130. The tank galley 132 returns hydraulic fluid to thehydraulic fluid tank 112, where it is available to be re-pumped. Thevalves 114 also include a hydraulic connection between the open centercore 130 and the power core 138, namely, an open center/power corepassage 140. Typically, the valves 114 may also include smaller internalvalves utilized to prevent, for example, overpressure or incorrect flowdirection in the system, such as relief valves 142, or load drop checkvalves 144, which are not material to the explanation of the prior artor the invention.

The prior art open center hydraulic valve system 110 is typically housedin a standard manifold (not illustrated) attached to the equipment(e.g., construction, earth moving, or forestry equipment, such as abackhoe) in which the open center hydraulic valve system 110 is beingused. The fixed displacement pump 116 is typically driven by a powertake-off (not illustrated), which, in turn, is directly mounted to atransmission (not illustrated), which is connected to the prime mover ofthe equipment in which the prior art open center hydraulic valve system110 is being used.

The operation of the spools 118 in each of the valves 114 to directhydraulic fluid flow to and to permit fluid flow from associatedhydraulic ports 122 and 124 to cause, for example, a piston to movewithin a cylinder and thereby cause movement of a functional aspect ofthe equipment on which the open center hydraulic valve 110 is mounted iswell-known to skilled practitioners, and can be ascertained by skilledpractitioners by reference solely to the schematic diagram found inFIG. 1. For purposes of the following explanation, hydraulic ports 122and 124 will be assumed to be hydraulically connected to a cylinder 126above and below a piston 128, respectively, in a manner similar to thatillustrated in FIGS. 2A, 2B, and 2C.

As can be seen in FIGS. 1, and will be described further below, when aspool 118 is caused by spool actuator 120 to be in the neutral position(with the open center core 130 unrestricted by the spool 118, and thefluid passageways between either the open center core 130 or the tankgalley 132, on the one hand, and the pair of hydraulic ports 122 and 124associated with the spool 118, on the other hand, being obstructed bythe spool 118, no net hydraulic fluid flows to or from the hydraulicports 122 and 124 to the cylinder 126 on either side of the piston 128,and thus, the piston 128 does not move. Instead, the hydraulic fluiddelivered at a constant flow rate (for a given engine speed) by thefixed displacement pump 116 flows unrestricted through the open centercore 130 and through the open center of the spools 118 to the tankgalley 132 and to the hydraulic fluid tank 112 where it is re-pumped.Hence, the function to which the piston 128 and cylinder 126 isassociated (e.g., the position of the boom) does not change, becausethere is no net change in hydraulic fluid in the cylinder 126 eitherabove or below the piston 128. The piston 128 therefore does not move.

If, as shown in FIG. 1, the spool actuator 120 is activated by anoperator to cause the spool 118 to move from the neutral position to afirst non-neutral position, the constant flow of hydraulic fluiddelivered by the fixed displacement pump 116 is caused by the partialrestriction by the spool 118 of the open center core 130 to increase inpressure. Referring to FIG. 1, the increase in fluid pressure in theopen center core 130 is communicated to the power core 138 through theopen center/power core passage 140. As shown in FIG. 1, the activatedspool 118 allows pressurized hydraulic fluid to flow from the power core138 to the first hydraulic port 122 associated with the activated spool118 into the cylinder 126 under the piston 128. The activated spool 118simultaneously allows fluid to flow out of the cylinder 126 through thesecond hydraulic port 124 associated with the activated spool 118 whichis connected above the piston 128. That fluid flows through the tankgalley 132 to the hydraulic fluid tank 112 (where it is re-pumped).Thus, the net effect is that hydraulic fluid under pressure flows intothe cylinder 126 below the piston 128, and hydraulic fluid flows out ofthe cylinder 126 above the piston 128. This causes the piston 128 andassociated load 134 to rise and the function to change (e.g., it causesthe boom and any associated load to rise).

On the other hand, if, as shown in FIG. 1, the spool operatormanipulates the actuator 120 to cause the spool 118 to move from theneutral position to a second non-neutral position, that once againcauses partial restriction of the open center 130, and causes the fluidflowing through the open center core 130 to increase in pressure. Thatincrease in hydraulic pressure is once again communicated from the opencenter core 130 to the power core 138 through open center/power corepassage 140. At the same time, hydraulic fluid is allowed by theactivated spool 118 to flow out of the cylinder 126 under the piston 128through the connected hydraulic port 122 associated with activated spool118 and through the tank galley 132 to the hydraulic fluid tank 112.Also at the same time, the spool directs pressurized fluid (underpressure from the fixed displacement pump 116 due to partial restrictionof the opening in the open center core 130 by the spool 118) to flowfrom the power core 138 through the associated hydraulic port 124 intothe cylinder 126 above the piston 128. Thus, hydraulic fluid underpressure is introduced to the cylinder 126 above the piston 128, andhydraulic fluid is drained from the cylinder 126 below the piston 128.This causes the piston 128 to lower and the equipment function to change(e.g., the boom and any associated load is caused to lower). A skilledartisan would recognize, of course, that this activation of spools 118in the valves 114 can be utilized to operate a number of differentequipment functions having moving components, and would not be limitedto booms (or to backhoes).

Further details of the operation of the prior art open center hydraulicvalve system 110 illustrated in FIG. 1 are described below. Theexplanation herein concerning the operation of a single spool 118 (andits associated pair of hydraulic ports 122 and 124) within a singlevalve 114 associated with a particular single function is illustrative,and is not limited to that particular single spool 118 or valve 114, andapplies to other spools 118 and valves 114 within the open centerhydraulic valve system 110 as well.

Because the pump for the prior art open center hydraulic system 110 is afixed displacement pump 116, the flow of the hydraulic fluid supplied bythe fixed displacement pump 116 is constant for a given engine speed forthe equipment in which the prior art open center hydraulic system 110 ismounted.

When the spool actuators 120 in the valves 114 in the prior art opencenter hydraulic system 110 are in the neutral position, all of theassociated spools 118 are likewise in the neutral position. Asillustrated in FIG. 1, the centers of the valve spools 118 are open, thenet flow paths to the associated hydraulic ports 122 and 124 (from theopen center core 130 or the power core 138), or from the hydraulic ports122 and 124 (to the tank galley 132), are blocked by the spools 118, andall net hydraulic fluid flow pumped by the fixed displacement pump 116from the hydraulic fluid tank 112 at a constant flow rate flowsunrestricted through the open center core 130 through the spools 118 tothe tank galley 132 and then back to the hydraulic fluid tank 112 whereit is again available to be pumped.

When one of the functions associated with the prior art open centerhydraulic system 110 is desired to be activated, the spool actuator 120associated with that function is activated by an equipment operator inorder to move the associated spool 118 (left or right, as shown in theschematic in FIG. 1) in order to partially restrict or “pinch” theopening through the open center core 130 to the tank galley 132. Thispartial restriction of hydraulic fluid flow by the spool 118 in the opencenter core 130 partially restricts flow to the tank galley 132, and, inturn, increases the pressure of the hydraulic fluid in the open centercore 130 being provided at constant flow by the fixed displacement pump116. The resulting increased hydraulic fluid pressure in the open centercore 130 is transmitted hydraulically through the open center/power corepassage 140 to the power core 138.

If the chosen spool actuator 120 is activated with the intention ofcausing the piston 128 to move to a first non-neutral position asillustrated in FIG. 1 (and to thereby, for example, lift a boom andassociated load), then not only is the open center core 130 partiallyrestricted to cause an increase in pressure to occur in the open centercore 130 and be transmitted to the power core 138, but the spool 118 atthe same time opens a hydraulic passage in the valve 114 betweenassociated hydraulic port 122 (hydraulically connected to a cylinder 126below the piston 128, in the manner illustrated in FIG. 2B) and thepower core 138. The hydraulic fluid, having increased hydraulic pressurein the power core 138, is transmitted through associated hydraulic port122. Simultaneously, activated spool 118 opens a hydraulic passage inthe valve 114 between associated hydraulic port 124 (hydraulicallyconnected to a cylinder 126 above the piston 128, in the mannerillustrated in FIG. 2B) and the tank galley 132. The result is thathydraulic fluid under pressure from the power core 138 flows throughassociated hydraulic port 122 and begins filling the cylinder 126 belowthe piston 128, and hydraulic fluid is permitted to leave the cylinder126 above the piston 128 by flowing through associated hydraulic port124 into the tank galley 132 to return to the hydraulic fluid tank 112,where it is available to be re-pumped. By adding pressurized hydraulicfluid to the cylinder 126 below the piston 128, and by reducinghydraulic fluid in the cylinder 126 above the piston 128, the piston 128and its associated load 134 is lifted.

Conversely, if the chosen spool actuator 120 is activated with theintention of causing the piston to move to a second non-neutral positionas illustrated in FIG. 1, (and to, for example, cause a boom to lower),then not only does the activated spool 118 cause the open center core130 to be partially restricted to cause an increase in fluid pressure inthe open center core 130 to be hydraulically transmitted to the powercore 138 via open center/power core passage 140, but also the activatedspool 118 opens a hydraulic passage in the valve 114 between theassociated hydraulic port 124 (hydraulically connected to cylinder 126above the piston 128) and the power core 138 (with pressurized hydraulicfluid). Simultaneously, the activated spool 118 opens a passage in valve114 between associated hydraulic port 122 (hydraulically connected tocylinder 126 below the piston 128, in the manner illustrated in FIG. 2C)and the tank galley 132, allowing hydraulic fluid to flow out of thecylinder 126 below the piston 128 to the tank galley 132 and thehydraulic fluid tank 112. The result is that hydraulic fluid underpressure from the power core 138 begins filling the cylinder 126 abovethe piston 128, and hydraulic fluid begins leaving the cylinder 126below the piston 128. The piston 128 and its associated load 134 lowers(in this example, the boom and load is lowered).

Because the prior art open center hydraulic valve system 110 illustratedin FIG. 1 utilizes a fixed displacement pump 116 operating at a constantflow for a given engine speed for the equipment on which it is mounted,all power used to generate unused hydraulic fluid flow (such ashydraulic fluid constantly flowing through the open center core 130 whenthe spools 118 are in the neutral position) is a loss. Nevertheless, thesize and power of the fixed displacement pump 116 in such a prior artsystem must accommodate not only sufficient hydraulic flow and systempressure to operate the multiple functions operated by the valves 114 atrated load conditions, but also must sustain the constant hydraulic flowthrough the open center core 130 (as well as overcome line losses) inorder for the system to operate properly. A relatively large andpowerful fixed displacement pump 116 running constantly is thereforerequired for the prior art open center hydraulic valve system 110. And,as noted above, a considerable portion of the power of the fixeddisplacement pump 116 in such a system is required to deliver hydraulicfluid flow that is frequently unused by the functions of the system, forexample, the unused flow that constantly passes through the open centercore 130 to the hydraulic fluid tank 112, only to be re-pumped (when oneor more, often all, spools 118 are not activated and the functions areidle). Hence, significant inefficiencies are inherent in the prior artopen center hydraulic valve system 110.

A number of factors have spurred equipment manufacturers and hydraulicsystems designers to attempt to overcome the inefficiencies andshortcomings of the prior art prior art hydraulic valve systems,including open center hydraulic valve system 110. New emissionsstandards and a desire for fuel savings have caused designers andmanufacturers to attempt to design equipment and hydraulic systems thatare more fuel efficient, and more power efficient, by achieving greaterhorsepower management. Manufacturers and designers likewise desire toavoid significant increases in the size, weight, and expense ofproviding alternatives to the prior art systems, such as open centerhydraulic valve systems 110.

For example, one potential alternative previously considered bydesigners and manufacturers was to replace the fixed displacement pump116 of the open center hydraulic valve system 110 illustrated in FIG. 1with a variable displacement piston pump (not illustrated). In such apotential alternative, however, the existing valves 114 in the prior artopen center hydraulic valve system 110 would be required to be replacedby considerably larger, considerably heavier, and considerably moreexpensive valves in order to permit the higher hydraulic fluid flowrequired by such a replacement. Such a potential alternative thereforenot only was largely rejected as being cost prohibitive, but theinstallation of such a large, heavy system was determined to be highlyundesirable because, in many if not most applications, there is limitedroom available on equipment for the hydraulic system to be mounted.

The present invention, known as a fixed/variable hybrid system,overcomes the problems associated with both the prior art open centerhydraulic valve system 110 and the potential alternatives that have beenconsidered and largely rejected (for example, replacement of the fixeddisplacement pump 116 with a variable displacement piston pump). Thefixed/variable hybrid system of the present invention achieves reducedemissions, greater horsepower management, and greater fuel savings,without greatly increasing the cost, size, or weight of the hydraulicvalve system.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the embodiments of theinvention described herein to provide a hydraulic valve system, called afixed/variable hybrid system, that overcomes the shortcomings of priorart open center hydraulic valve systems, while still achieving thefunctions and benefits of prior systems.

It is another object of the embodiments of the fixed/variable hybridsystem invention described herein to provide a hydraulic valve systemcapable of hydraulically operating the functions of heavy off-roadequipment, such as earth moving, construction, and forestry equipment,while simultaneously significantly reducing unused hydraulic flow, andthereby significantly reducing the inefficient use of power associatedwith such unused flow.

It is yet another object of the embodiments of the fixed/variable hybridsystem invention described herein to achieve substantially decreasedfuel emissions, and substantially increased fuel savings, by reducinginefficient equipment engine usage resulting from power consumptionrequired to provide inefficient hydraulic fluid flow associated withprior art hydraulic systems, such as open center hydraulic valvesystems.

Still another object of the embodiments of the fixed/variable hybridsystem invention described herein is to achieve the above objects in amanner that is not cost prohibitive, but rather in a manner that iscost-efficient.

A further object of the embodiments of the invention described herein isto achieve the foregoing objects without greatly increasing the size orweight of the hydraulic valve system, as compared to prior art systemssuch as the open center hydraulic valve system previously discussed.

The disclosed embodiments of the present fixed/variable hybrid systeminvention achieve the aforementioned objects and others because theyinclude features and combinations not found in prior art hydraulic valvesystems, and, in particular, not found in prior art open centerhydraulic valve systems.

In the described embodiments of the present invention, an improvedhydraulic valve system, called a fixed/variable hybrid system, isprovided, wherein the need for a relatively large and inefficient fixeddisplacement pump to hydraulically power such a system is eliminated.Instead, the fixed/variable hybrid system of the present invention usesmodified constant flow open center valve banks (“fixed/variable valves”)in conjunction with a relatively small fixed displacement pump coupledwith a variable displacement piston pump. The small fixed displacementpump provides hydraulic fluid to an open center core, and also via anopen center/power core passage through a check valve to thefixed/variable valves' power cores. The small fixed displacement pump isalso ported through a sense signal passage to the load sense signal portof the variable displacement pump. The variable displacement pump, inturn, provides hydraulic fluid flow to one or more fixed/variable valvesdirectly through the fixed/variable valves' power core. Flow from thevariable displacement pump to the open center core is blocked by thecheck valve in the open center/power core passage.

When a particular spool actuator is selected and activated, the selectedspool moves to partially restrict or “pinch” the hydraulic fluid flowgenerated by the small fixed displacement pump through the open centercore. The partial flow restriction caused by the spool in the opencenter core causes fluid pressure to rise in the hydraulic fluid flowprovided by the small fixed displacement pump into the open center core.The rise in hydraulic fluid pressure in the open center core iscommunicated from the open center core through the sense signal passageto the load sense signal port of the variable displacement pump.Depending on the pressure of the hydraulic fluid pressure receivedthrough the load sense signal port (for example, depending on how manyspools have been activated causing partial restrictions in the opencenter core, and thereby causing increases in fluid pressure to betransmitted from the open center core via the sense signal passage tothe load sense signal port), the increased fluid pressure received inthe load sense signal port of the variable displacement piston pumpcauses the variable displacement piston pump to variably increase itsfluid flow to the fixed/variable valves' power cores.

Stated another way, the variable displacement piston pump is responsiveto an increase or decrease in fluid pressure transmitted from the opencenter core through the sense signal passage to the load sense signalport associated with the variable displacement piston pump. The greaterthe fluid pressure received by the load sense signal port from the smallfixed displacement pump through the open center core via the sensesignal passage, the more that the variable displacement piston pumpincreases its flow and pressure to the power core, and vice-versa(within the limitations of the variable displacement piston pump). Thesmall fixed displacement pump also may supply some pressurized hydraulicfluid to the power core through the open center/power core passage. Thecheck valve in the open center/power core passage prevents reverse flowonce the pressure in the power core exceeds the pressure in the opencenter core.

The spools in the fixed/variable valves of the fixed/variable hybridsystem are the same as those used in the prior art open center hydraulicvalve system, and thus, when activated, operate in the same manner todirect fluid flow from the power core (and to the tank galley) throughthe pair of hydraulic ports associated with a particular activatedspool. As illustrated in schematic diagram in FIG. 3, pressurizedhydraulic fluid flow from the power core may be selectively directed byan activated spool to one of a pair of selected hydraulic portsassociated with the activated spool. At the same time, hydraulic fluidis permitted to flow from the other hydraulic port associated with theactivated spool to the tank galley and to the hydraulic fluid tank.

By eliminating altogether the relatively large fixed displacement pumpof the prior art system (which operated constantly and inefficiently ata full and fixed flow), and by substituting a relatively small fixeddisplacement pump, significant efficiencies are achieved by thefixed/variable hybrid system invention. The small fixed displacementpump is sufficient to provide an increase in hydraulic pressure to theload sense signal port of the variable displacement piston pump (but notnecessarily to operate the hydraulic functions associated with thesystem). Operation of the hydraulic functions is mainly achieved by thevariable displacement piston pump operating at higher flow and providingincreased hydraulic pressure only when activated by the increase inhydraulic pressure received by the load sense signal port, as providedby the small fixed displacement pump. In other words, the variabledisplacement piston pump operates at a higher flow only as required, notconstantly as in the case of the relatively large fixed displacementpump of the prior art, including the open center hydraulic valve system.

As a result, significant fuel savings and power efficiencies areachieved by the present invention. Simply put, the fixed/variable hybridsystem invention described herein utilizes a considerably smaller fixeddisplacement pump than prior art systems, resulting in less power beingwasted pumping hydraulic fluid that is not operating any of thehydraulic functions (e.g., the boom) of the equipment (e.g., a backhoe),such as when the spools of the fixed/variable valves associated with thehydraulic functions are in a neutral position. Instead, thefixed/variable hybrid system utilizes only a small constant flowprovided by a small fixed displacement pump, which in turn provides asignal in the form of a pressurized hydraulic fluid through a sensesignal passage to a load sense signal port of a variable displacementpiston pump to increase fluid flow to power core of the system only asneeded upon demand when spool actuators (and their associated spools)are activated to operate an equipment function. Thus, the vast majorityof operational power for the fixed/variable hybrid system is utilizedonly as needed, achieving significant fuel, power, and emissionefficiencies. Moreover, the invention's fixed/variable hybrid systemdoes not require any major design overhaul for the fixed/variablevalves, or increase in size and weight of the fixed/variable valves, orsignificant increase in cost of the fixed/variable valves, as would berequired if a variable displacement piston pump were to be merelysubstituted for the fixed displacement pump of the prior art open centerhydraulic valve system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of an embodiment of a prior art opencenter hydraulic valve system having two valves, eight spools, and eightfunctions corresponding to the spools.

FIG. 2A is a cross-sectional view illustrating the operation of a spoolof a prior art simple CFO valve in the neutral position.

FIG. 2B is a cross-sectional view illustrating the operation of a spoolof a prior art simple CFO valve activated in a non-neutral firstposition to lift a load.

FIG. 2C is a cross-sectional view illustrating the operation of a spoolof a prior art simple CFO valve activated in a non-neutral secondposition to lower a load.

FIG. 3 is a schematic drawing of an embodiment of the fixed/variablehybrid system of the present invention, having two fixed/variablevalves, eight spools, and eight functions corresponding to the spools.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the fixed/variable hybrid system 210 of the presentinvention is illustrated schematically in FIG. 3 in a manner usingschematic symbols that would be understood by persons skilled in theart.

Referring to FIG. 3, the fixed/variable hybrid system 210 includes ahydraulic fluid tank 212, one or more standard open center hydraulicvalve banks modified in the manner described and illustrated herein(“fixed/variable valves”) 214, a small fixed displacement pump 216, anda variable displacement piston pump 246. Each fixed/variable valve 214may include one or more spools 218, each activated by an associatedspool actuator 220. As previously discussed, the spool actuator 220 maybe activated by an operator using a variety of known means, includingmechanically, electrically, hydraulically, pneumatically, or otherwise.

The fixed/variable hybrid system 210 of the present invention may behoused in a standard manifold (not illustrated) attached to theequipment (e.g., off-road construction, earth moving, or forestryequipment—not illustrated) in which the fixed variable hybrid system 210is being used. The small fixed displacement pump 216 and variabledisplacement piston pump 246 may be driven by a power take-off (notillustrated), which, in turn, is mounted to a transmission (notillustrated) connected to the prime mover of the equipment.

Each spool 218 of the fixed/variable hybrid system 210 in FIG. 3operates in the same manner as described above for spools 118 in theprior art open center hydraulic valve system 110 to provide selectivehydraulic communication with hydraulic ports 222 and 224 associated witheach spool 218. In a typical application of the invention, each pair ofhydraulic ports 222 and 224 communicate hydraulically with a cylinder onopposite sides of a piston to cause piston movement, in a manner similarto that described above for the open center hydraulic valve system 110.In order to prevent undue repetition, to serve the function of brevity,and to avoid belaboring what is known to skilled practitioners in theart, the operation of the hydraulic ports 222 and 224 hydraulicallyconnected to a cylinder on either side of a load-supporting piston inthe fixed/variable hybrid system 210 is the same as explained andillustrated for hydraulic ports 122 and 124 hydraulically connected tothe cylinder 126 on either side of piston 128, and load 134 in the priorart open center hydraulic valve system 110 previously described andillustrated (see, e.g., FIGS. 1, 2A, 2B, and 2C).

Referring once again to FIG. 3, each spool 218 and associated pair ofhydraulic ports 222 and 224 of the fixed/variable valve 214 isassociated with a function to be performed by the equipment on which thefixed/variable hybrid system 210 is mounted. Once again, in FIG. 3, theassociated functions that are illustrated are those commonly associatedwith a backhoe: boom, bucket, stick, swing, stabilizer, boom loader,bucket loader, and auxiliary, although skilled practitioners wouldrecognize that the above functions and equipment associated with thefixed/variable hybrid system 210 are provided for illustration purposes,and can vary considerably in actual applications.

An open center core 230 flows through the spools 218 of thefixed/variable valves 214. The fixed/variable valves 214 also include apower core 238 for hydraulic communication of pressurized hydraulicfluid, and a tank galley 232 for return of hydraulic fluid to thehydraulic fluid tank 212 where it becomes available to be re-pumped.Importantly, the provision of hydraulic fluid to the power core 230 ofthe fixed/variable hybrid system 210 (see FIG. 3) differs significantlyfrom the power core 130 of the open center hydraulic valve system 110(see FIG. 1). The power core 230 of the fixed/variable hybrid system 210(see FIG. 3) is ported directly through each fixed/variable valve 214 tothe output of variable displacement piston pump 216. This is not true ofthe power core 130 of the prior art open center hydraulic valve system110 (see FIG. 1). Referring again to FIG. 3, an open center/power corepassage 240 hydraulically connects the open center core 230 and thepower core 238. A check valve 248 is located in or adjacent to the opencenter/power core passage 240 permitting fluid flow in the opencenter/power core passage 240 from the open center core 230 to the powercore 238, but obstructing fluid flow in the opposite direction when thefluid pressure in the power core 238 exceeds that in the open centercore 230.

The small fixed displacement pump 216 pumps hydraulic fluid (at aconstant rate for a given engine speed) from the hydraulic fluid tank212 to the open center core 230. As has been discussed, and will befurther explained below, the small fixed displacement pump 216 in thefixed/variable hybrid system 210 of the invention is considerablysmaller, less expensive, requires less fuel and energy consumption, andthus results in less fuel emissions for a given equivalent equipmentapplication than the relatively larger fixed displacement pump 116 ofthe prior art open center hydraulic valve system 110.

A variable displacement piston pump 246 pumps hydraulic fluid (at avariable rate, as further explained herein) directly to the power core238 of each of the fixed/variable valves 214. Associated with thevariable displacement piston pump 246 is a load sense signal port 250.The load sense signal port 250 is hydraulically connected to a sensesignal passage 252, which, in turn, is hydraulically connected to theopen center core 230, preferably between the small fixed displacementpump 216 and the first spool 218 to which the small displacement pump216 is hydraulically connected. The load sense signal port 250 regulatesthe hydraulic flow output of the variable displacement piston pump 246such that as the hydraulic fluid pressure delivered by the sense signalpassage 252 to the load sense signal port 250 from the open center core230 increases, the output flow of hydraulic fluid from the variabledisplacement piston pump 246 to the power core 238 increases (within theoutput limits of the variable displacement piston pump 246). Conversely,as the hydraulic fluid pressure delivered by the sense signal passage252 to the load sense signal port 250 from the open center core 230decreases, the output flow of hydraulic fluid from the variabledisplacement piston pump 246 to the power core 238 decreases (within theoutput limits as well).

The fixed/variable valves 214 may also preferably include smallerinternal valves, such as relief valves 242, or load drop check valves244, in order to avoid overpressure or incorrect flow direction in thefixed/variable hybrid system 210 of the invention. The inclusion ofthose smaller valves are illustrated and are preferable, but theoperation and function of those valves would be understood by a skilledpractitioner, and an explanation of the smaller valves would not bematerial to an understanding of the invention.

The invention's fixed/variable hybrid system 210 illustrated in FIG. 3operates as described below. When all of the spools 218 of thefixed/variable valves 214 are in the neutral position, the open centercore 230 is unrestricted by the spools 218, and, at the same time, eachof the spools 218 prevent net fluid flow between their respectiveassociated hydraulic ports 222 and 224, on the one hand, and the powercore 238 or the tank galley 232, on the other hand. In that condition,the small fixed displacement pump 216 pumps hydraulic fluid from thehydraulic fluid tank 212, and provides the full constant (for a givenengine speed) fluid flow of the small fixed displacement pump 216through the open center core 230 in an unrestricted manner through thespools 218 of the fixed/variable valves 214, and then to the tank galley232, returning to the hydraulic fluid tank 212. The power required tooperate the small fixed displacement pump 216 is considerably smallerfor a given equivalent application as compared to the power required torun the significantly larger fixed displacement pump 116 of the priorart open center hydraulic valve system 110. Thus, less inefficiencyoccurs as a result of the constantly running small fixed displacementpump 216 (for example, when the spools 218 of the fixed/variable valves214 are all in the neutral position), because less fuel and powerconsumption occurs, and less fuel emissions are generated.

When the spools 218 are all in the neutral position, the hydraulic fluidpressure communicated from the open center core 230 through the sensesignal passage 252 to the load sense signal port 250 associated with thevariable displacement piston pump 246 is at a minimum, and thus thehydraulic fluid flow provided by the variable displacement piston pump246 is also at a minimum. In this condition, the check valve 248 in theopen center/power core passage 240 may permit some fluid flow from theopen center core 230 through the open center/power core passage 240 tothe power core 238 until the hydraulic fluid pressure in the power core238 exceeds the pressure in the open center core 230, closing checkvalve 248.

When an operator chooses to operate a hydraulic function of theequipment on which the fixed/variable hybrid system 210 is mounted, theoperator directly or indirectly manipulates the spool actuator 220associated with that function. The chosen spool actuator 220 operates aspool 218 associated with that spool actuator 220.

If the operator chooses to cause the spool 218 to move to a firstnon-neutral position, movement of the spool 218 causes several things tooccur. Movement of the 218 spool causes a partial restriction of theopen center core 230. Because hydraulic fluid is being provided to theopen center core 230 at a constant fluid flow by the small fixeddisplacement pump 216, the hydraulic pressure in the open center core230 increases upstream of the activated spool 218 (that is, between thatactivated spool 218 and the small fixed displacement pump 216) that hascaused the partial restriction.

The increased hydraulic fluid pressure in the open center core 230 ishydraulically communicated via the sense signal passage 252 to the loadsense signal port 250. The increase in hydraulic pressure at the loadsense signal port 250 causes the variable displacement piston pump 246to increase its hydraulic fluid output, thus increasing the hydraulicpressure and flow in the power core 238 to which it is directlyconnected. Once again, the open center/power core passage 240 and itsassociated check valve 248 may permit some hydraulic fluid to flow fromthe partially restricted open center core 230 to the power core 238until such time as the pressure in the power core 238 exceeds thepressure in the now partially restricted (by the activated spool 218)open center core 230, closing check valve 248.

At the same time, when activated spool 218 is moved to the firstnon-neutral position, the spool 218 opens a hydraulic passage throughthe fixed/variable valve 214 between the power core 238 and the firsthydraulic port 222 associated with the activated spool 218, causinghydraulic fluid under pressure (delivered mainly by the variabledisplacement piston pump 246 through the power core 238) to flow fromthe power core 238 to the associated first hydraulic port 222. In thefirst non-neutral position, the activated spool 218 continues toobstruct the passage through the fixed/variable valve 214 between thepower core 238 and the second hydraulic port 224 associated with theactivated spool 218. In that first position, however, the activatedspool 218 opens a hydraulic passage through the fixed/variable valve 214between the tank galley 232 and the second hydraulic port 224 associatedwith the activated spool 218, permitting hydraulic fluid to flow fromthe second hydraulic port 224 through the tank galley 232 to thehydraulic fluid tank 212. At the same time, activated spool 218 in thefirst position obstructs the hydraulic fluid pathway between the tankgalley 232 and the first hydraulic port 222.

In an example where the first hydraulic port 222 associated with theactivated spool 218 is hydraulically connected to a cylinder at alocation below a piston, and the second associated hydraulic port 224 ishydraulically connected to a cylinder at a location above a piston, thehydraulic fluid under pressure flows into the cylinder through the firstassociated hydraulic port 222 below the piston, and hydraulic fluidflows out of the cylinder through the second associated hydraulic port224 above the piston, causing the piston (and associated load) to rise.If, in this example, the operator has chosen the spool actuator 220associated with the boom on a backhoe, the fixed/variable hybrid system210 would cause the backhoe's boom to rise.

If, on the other hand, the operator chooses to use a spool actuator 220to cause the spool 218 to move in a second non-neutral position (e.g.,in a non-neutral position opposite from the first direction), movementof the activated spool 218 in the second non-neutral position once againcauses several results. Movement of the activated spool 218 to a secondnon-neutral position would again cause a partial restriction of the opencenter core 230 of the fixed/variable valve 214. The constant fluid flowprovided by the small fixed displacement pump 216 through thenow-partially restricted open center core 230 causes the fluid pressureto increase in the open center core 230 between the activated spool 218and the small fixed displacement pump 216.

The sense signal passage 252 hydraulically communicates the increase inhydraulic fluid pressure from the open center core 230 through the sensesignal passage 252 to the load sense signal port 250 associated with thevariable displacement piston pump 246. This causes the variabledisplacement piston pump 246 to increase the rate of hydraulic fluidoutput to the power core 238 to which it is directly connected,increasing the hydraulic pressure therein. Also, some hydraulic fluidmay flow from open center core 230 through the open center/power corepassage 240 and its associated check valve 248 to the power core 238until the pressure in the power core 238 exceeds the pressure in theopen center core 230, closing check valve 248.

When the operator causes spool 218 to move to the second non-neutralposition, the activated spool 218 is moved so that, in addition to thepartial restriction of the open center core 230 described above, theactivated spool 218 moves to a position where a hydraulic passagethrough the fixed/variable valve 214 is opened between the power core238 and the second hydraulic port 224 associated with the activatedspool 218, causing the hydraulic fluid under pressure in the power core238 (delivered mostly by the increased fluid flow from the variabledisplacement piston pump 216) to flow from the power core 238 to theassociated second hydraulic port 224. The activated spool 218, in thesecond position, obstructs the hydraulic passage through thefixed/variable valve 214 between the power core 238 and the firsthydraulic port 222 associated with the activated spool 218. Theactivated spool 218 also obstructs the hydraulic fluid pathway betweenthe tank galley 232 and the second hydraulic port 224 associated withthe activated spool 218. But in the second non-neutral position, theactivated spool 218 opens a hydraulic passage through the fixed/variablevalve between the tank galley 232 and the first hydraulic port 222associated with the activated spool 218, allowing hydraulic fluid toflow from the first hydraulic port 222 associated with the activatedspool 218 through the tank galley 232 to the hydraulic fluid tank 212.

If the hydraulic ports are hydraulically connected to a cylinder havinga piston in the manner described in the previous example, that is, withthe first hydraulic port 222 associated with the activated spool 218being connected below the piston, and the second hydraulic port 224associated with the activated spool 218 being connected above thepiston, then hydraulic fluid under pressure will flow from the powercore 238 through the second hydraulic port 224 associated with theactivated spool 218 into the cylinder above the piston, and hydraulicfluid will flow out of the cylinder below the piston through the firsthydraulic port 222 associated with the activated spool 218 via the tankgalley 232 to the hydraulic fluid tank 212. The increase in hydraulicfluid in the cylinder above the piston and decrease in hydraulic fluidin the cylinder below the piston will cause the piston, and anyassociated load, to lower. If, as in the previous example, the operatorchose to activate (via a spool actuator 220) the spool 218 associatedwith a boom, that boom, as powered by the fixed/variable hybrid system210 of the invention, would lower.

While a single spool actuator 220 associated with a single spool 218associated with a single function was provided as an example toillustrate the operation of the fixed/variable hybrid system 210,persons skilled in the art will recognize that different spools 218associated with different functions may be activated in the same manner,and those will not be separately discussed.

In the event that more than one spool 218 is activated at the same timein the fixed/variable hybrid system of the present invention, furtherpartial restriction of the open center core 230 would occur because ofthe multiple partial restrictions resulting from multiple activatedspools 218. The further partial restrictions of the open center core 230of the constant fluid flow (for a given engine speed) provided by thesmall fixed displacement pump 216 would cause the fluid pressure in theopen center core 238 to further increase to a pressure greater than thepressure occurring when only one spool 218 was activated. Stated anotherway, more activated spools 218 cause greater partial restrictions in theopen center core 238 resulting in greater fluid pressure within the opencenter core 238. This greater fluid pressure in the open center core 238is communicated hydraulically via the sense signal passage 252 to theload sense signal port 250 of the variable displacement piston pump 246.

As discussed previously, greater fluid pressure received by the loadsense signal port 250 causes the variable displacement piston pump 246to increase its hydraulic fluid flow output to the power core 238,increasing the fluid flow and pressure in the power core 238. Thisincrease in pressure in the power core 238 serves to hydraulically powerthe various functions of the multiple activated spools 218.

When multiple spools 218 are activated, once again, some fluid flow mayoccur from the open center core 230 through the open center/power corepassage 240 and its associated check valve 248 to the power core 238until the point that the pressure in the power core 238 exceeds thepressure in the open center core 230, closing check valve 248.

The advantages of the embodiments of the fixed/variable hybrid system210 invention herein are significant. The inefficiencies of prior arthydraulic systems, such as the prior art open center hydraulic valvesystem 110, are largely overcome. Instead of a relatively large fixeddisplacement pump 116 operating constantly at a fixed rate, consumingpower and fuel, and causing emissions, at the constant rate required bythe relatively large fixed displacement pump 116, the fixed/variablehybrid system 210 utilizes a relatively small fixed displacement pump216, consuming considerably less power and fuel, and therefore emittingconsiderably less fuel emissions.

The prior art fixed displacement pump 116 needed to generate sufficienthydraulic fluid flow (needed to be sufficiently large and powerful) tooperate all equipment functions (multiple functions at one time) atrated load, and to satisfy line losses. That larger pump was required torun at full and constant flow at all times during operation. The smallfixed displacement pump 216 of the present invention only needs to besufficiently large to generate a hydraulic pressure increase(essentially, a hydraulic pressure signal) through the sense signalpassage 252 to the load sense signal port 250 (and to satisfy linelosses), therefore, only a small fixed displacement pump 216 is requiredto run constantly. Hydraulic fluid flow to power the functions of theequipment is supplied only on an “as needed” basis by the variabledisplacement piston pump 246, resulting in considerable savings in fuel,and considerable reduction in emissions (as a result of running theengine to power the respective pumps). This is especially important asthe rated load capacities increase for the equipment in which thefixed/variable hybrid system 210 is used.

Moreover, unlike other potential alternatives that seek to overcome theshortcomings of the prior art, such as mere substitution of a variabledisplacement piston pump for a fixed displacement pump in an open centerhydraulic valve system, the fixed/variable hybrid system 210 of thepresent invention does not require redesigning or other major overhaulsof the design of the constant flow open center valve banks to greatlyincrease the size of the valves. This potential alternative has inherentsignificant problems due to the limited space available for hydraulicvalve systems on the equipment on which it is typically mounted. Statedanother way, bulky and heavy potential alternatives are not acceptablebecause they often will not fit on the equipment on which they arerequired. Furthermore, the considerable added expense of the requiredresized valves for such a system makes such a potential alternativehighly undesirable.

In sum, the fixed/variable hybrid system 210 of the present invention isa significant improvement over the prior art, and is superior to otheralternatives seeking to overcome the shortcomings of the prior art. Thepresent invention provides significant benefits in fuel efficiency,horsepower management, decreased emissions, reduced cost of manufacture(compared to resized/redesigned valves), and reduced size/weight(compared to resized/redesigned valves).

While the above-described embodiments of the fixed/variable hybridsystem 210 invention have been found and are believed to be useful andpreferable, particularly in certain application using the invention inconnection with off-road earth moving, construction, and forestryequipment, skilled practitioners will recognize that other combinationsof elements, dimensions, or materials can be utilized, and otherequipment applications can be realized, without departing from theinvention claimed herein. Moreover, although certain embodiments of theinvention have been described by way of example, it will be understoodby skilled practitioners that modifications may be made to the disclosedembodiments without departing from the scope of the invention, which isdefined by the claims.

Having thus described exemplary embodiments of the invention, that whichis desired to be secured by Letters Patent is claimed below.

I claim:
 1. A fixed/variable hybrid system for operation of hydraulicequipment, comprising: (1) one or more fixed/variable valves, with eachof the fixed/variable valves having one or more spools; (2) a fixeddisplacement pump, which pumps hydraulic fluid at a constant rate from ahydraulic fluid tank, and which is hydraulically connected to an opencenter core in each of the fixed/variable valves; (3) a variabledisplacement piston pump, having associated therewith a load sensesignal port, wherein the variable displacement piston pump pumpshydraulic fluid at a variable rate from the hydraulic fluid tank to apower core in each of the fixed/variable valves, and wherein an increasein hydraulic fluid pressure received by the load sense signal portcauses the variable displacement piston pump to pump hydraulic fluid atan increased rate, and wherein a decrease in hydraulic fluid pressurereceived by the load sense signal port causes the variable displacementpiston pump to pump hydraulic fluid at decreased rate; (4) a tank galleyin each of the fixed/variable valves that delivers hydraulic fluid tothe hydraulic fluid tank; (5) an open center/power core passagehydraulically connecting the open center core and the power coreassociated with each of the fixed/variable valves, wherein, for each ofthe fixed/variable valves, the hydraulic connection between the opencenter core and the open center/power core passage is located betweenthe fixed displacement pump and the first spool of the firstfixed/variable valve downstream of the fixed displacement pump in theopen center core; (6) a sense signal passage hydraulically connectingthe open center core and the load sense signal port, wherein thehydraulic connection between the sense signal passage and the opencenter core is located between the fixed displacement pump and the firstspool of the first fixed/variable valve downstream of the fixeddisplacement pump in the open center core; (7) wherein the open centercore is hydraulically connected to the tank galley downstream of thelast spool of the last fixed/variable valve downstream of the fixeddisplacement pump in the open center core; (8) wherein each spool ineach fixed/variable valve has associated therewith: (A) a firsthydraulic port and a second hydraulic port; (B) a first spool passagebetween the power core and the first hydraulic port associated with thespool, that is capable of being opened or closed depending upon theposition of the spool; (C) a second spool passage between the power coreand the second hydraulic port associated with the spool, that is capableof being opened or closed depending upon the position of the spool; (D)a third spool passage between the tank galley and the first hydraulicport associated with the spool, that is capable of being opened orclosed depending upon the position of the spool; (E) a fourth spoolpassage between the tank galley and the second hydraulic port associatedwith the spool, that is capable of being opened or closed depending uponthe position of the spool; (F) a fifth spool passage, wherein the opencenter core passes through the fifth spool passage, and wherein,depending upon the position of the spool, the spool may permit hydraulicfluid to flow through the fifth spool passage and the open center corein an unrestricted manner, or the spool may partially restrict thehydraulic fluid flowing through the fifth spool passage and the opencenter core; (9) wherein each spool has at least a neutral position, afirst non-neutral position, and a second non-neutral position, wherein:(A) in the neutral position, the spool permits hydraulic fluid to flowthrough the fifth spool passage and the open center core passingtherethrough in an unrestricted manner, and the spool blocks the flow ofhydraulic fluid through the first spool passage, the second spoolpassage, the third spool passage, and the fourth spool passage, (B) inthe first non-neutral position, the spool partially restricts the flowof hydraulic fluid through the fifth spool passage and the open centercore passing therethrough, the spool opens the first spool passagebetween the power core and the first hydraulic port associated with thespool allowing hydraulic fluid to flow from the power core to the firsthydraulic port, the spool opens the fourth spool passage between thetank galley and the second hydraulic port associated with the spoolallowing hydraulic fluid to flow from the second hydraulic port to thetank galley, the spool closes the second spool passage between the powercore and the second hydraulic port associated with the spool, and thespool closes the third spool passage between the tank galley and thefirst hydraulic port associated with the spool; and (C) in the secondnon-neutral position, the spool partially restricts the flow ofhydraulic fluid through the fifth spool passage and the open center corepassing therethrough, the spool opens the second spool passage betweenthe power core and the second hydraulic port associated with the spoolallowing hydraulic fluid to flow from the power core to the secondhydraulic port, the spool opens the third spool passage between the tankgalley and the first hydraulic port associated with the spool allowinghydraulic fluid to flow from the first hydraulic port to the tankgalley, the spool closes the first spool passage between the power coreand the first hydraulic port associated with the spool, and the spoolcloses the fourth spool passage between the tank galley and the secondhydraulic port associated with the spool; (10) wherein when activationof one or more of the spools of one or more of the fixed/variable valvesoccurs in a manner causing said one or more of the of the activatedspools to be in the first non-neutral position, each of the spools soactivated causes a partial restriction in the fifth spool passage ofeach of the activated spools in the first non-neutral position and inthe open center core passing therethrough, (A) causing the hydraulicfluid pumped at a constant rate by the fixed displacement pump throughthe open center core to increase in pressure between the fixeddisplacement pump and the one or more restrictions caused by each ofsaid activated spools that are in the first non-neutral position, (B)further causing the increased hydraulic fluid pressure in the opencenter core to be hydraulically communicated through the sense signalpassage to the load sense signal port, (C) with the increase inhydraulic fluid pressure received by the load sense signal port causingthe variable displacement piston pump to pump hydraulic fluid at anincreased rate to the power core of each of the fixed variable valves,increasing the hydraulic fluid flow and hydraulic fluid pressure in thepower core, (D) wherein each of the activated spools in the firstnon-neutral position permits hydraulic fluid in the power core havingincreased pressure to flow through the open first spool passage to thefirst hydraulic port associated with each activated spool in the firstnon-neutral position; and (11) wherein when activation of one or more ofthe spools of one or more of the fixed/variable valves occurs in amanner causing said one or more of the activated spools to be in thesecond non-neutral position, each of the spools so activated causes apartial restriction in the fifth spool passage of each of the theactivated spools in the second non-neutral position and in the opencenter core passing therethrough, (A) causing the hydraulic fluid pumpedat a constant rate by the fixed displacement pump through the opencenter core to increase in pressure between the fixed displacement pumpand the one or more restrictions caused by each of said activated spoolsthat are in the second non-neutral position, (B) further causing theincreased hydraulic fluid pressure in the open center core to behydraulically communicated through the sense signal passage to the loadsense signal port, (C) with the increase in hydraulic fluid pressurereceived by the load sense signal port causing the variable displacementpiston pump to pump hydraulic fluid at an increased rate to the powercore of each of the fixed variable valves, increasing the hydraulicfluid flow and hydraulic fluid pressure in the power core, (D) whereineach of the activated spools in the second non-neutral position permitshydraulic fluid in the power core having increased pressure to flowthrough the open second spool passage to the second hydraulic portassociated with each activated spool in the second non-neutral position.2. The fixed/variable hybrid system of claim 1 wherein the opencenter/power core passage further comprises a check valve that permitshydraulic fluid to flow through the open center/power core passage fromthe open center core to the power core when the hydraulic fluid pressurein the open center core exceeds the hydraulic fluid pressure in thepower core.
 3. The fixed/variable hybrid system of claim 2 wherein thecheck valve prevents hydraulic fluid from flowing through the opencenter/power core passage from the power core to the open center corewhen the hydraulic fluid pressure in the power core exceeds thehydraulic fluid pressure in the power core.
 4. The fixed/variable hybridsystem of claim 1 wherein the maximum pump output of the fixeddisplacement pump is less than the maximum pump output of the variabledisplacement piston pump.
 5. The fixed/variable hybrid system of claim 1wherein each of the spools in each of the fixed/variable valves hasassociated therewith a spool activator, wherein each of said spoolactivators is capable of causing movement of the spool associatedtherewith to either a neutral position, a first non-neutral position, ora second non-neutral position.
 6. A fixed/variable hybrid system foroperation of hydraulic equipment, comprising: (1) one or morefixed/variable valves, with each of the fixed/variable valves having oneor more spools; (2) a fixed displacement pump, which pumps hydraulicfluid at a constant rate from a hydraulic fluid tank, and which ishydraulically connected to an open center core in each of thefixed/variable valves; (3) a variable displacement piston pump, whereinthe variable displacement piston pump pumps hydraulic fluid at avariable rate from the hydraulic fluid tank to a power core in each ofthe fixed/variable valves; (4) a tank galley in each of thefixed/variable valves that delivers hydraulic fluid to the hydraulicfluid tank; (5) an open center/power core passage hydraulicallyconnecting the open center core and the power core associated with eachof the fixed/variable valves, wherein, for each of the fixed/variablevalves, the hydraulic connection between the open center core and theopen center/power core passage is located between the fixed displacementpump and the first spool of the first fixed/variable valve downstream ofthe fixed displacement pump in the open center core; (6) wherein theopen center core is hydraulically connected to the tank galleydownstream of the last spool of the last fixed/variable valve downstreamof the fixed displacement pump in the open center core; (7) wherein eachspool in each fixed/variable valve has associated therewith: (A) a firsthydraulic port and a second hydraulic port; (B) a first spool passagebetween the power core and the first hydraulic port associated with thespool, that is capable of being opened or closed depending upon theposition of the spool; (C) a second spool passage between the power coreand the second hydraulic port associated with the spool, that is capableof being opened or closed depending upon the position of the spool; (D)a third spool passage between the tank galley and the first hydraulicport associated with the spool, that is capable of being opened orclosed depending upon the position of the spool; (E) a fourth spoolpassage between the tank galley and the second hydraulic port associatedwith the spool, that is capable of being opened or closed depending uponthe position of the spool; (F) a fifth spool passage, wherein the opencenter core passes through the fifth spool passage, and wherein,depending upon the position of the spool, the spool may permit hydraulicfluid to flow through the fifth spool passage and the open center corein an unrestricted manner, or the spool may partially restrict thehydraulic fluid flowing through the fifth spool passage and the opencenter core; (8) wherein each spool has at least a neutral position, afirst non-neutral position, and a second non-neutral position, wherein:(A) in the neutral position, the spool permits hydraulic fluid to flowthrough the fifth spool passage and the open center core passingtherethrough in an unrestricted manner, and the spool blocks the flow ofhydraulic fluid through the first spool passage, the second spoolpassage, the third spool passage, and the fourth spool passage, (B) inthe first non-neutral position, the spool partially restricts the flowof hydraulic fluid through the fifth spool passage and the open centercore passing therethrough, the spool opens the first spool passagebetween the power core and the first hydraulic port associated with thespool allowing hydraulic fluid to flow from the power core to the firsthydraulic port, the spool opens the fourth spool passage between thetank galley and the second hydraulic port associated with the spoolallowing hydraulic fluid to flow from the second hydraulic port to thetank galley, the spool closes the second spool passage between the powercore and the second hydraulic port associated with the spool, and thespool closes the third spool passage between the tank galley and thefirst hydraulic port associated with the spool; and (C) in the secondnon-neutral position, the spool partially restricts the flow ofhydraulic fluid through the fifth spool passage and the open center corepassing therethrough, the spool opens the second spool passage betweenthe power core and the second hydraulic port associated with the spoolallowing hydraulic fluid to flow from the power core to the secondhydraulic port, the spool opens the third spool passage between the tankgalley and the first hydraulic port associated with the spool allowinghydraulic fluid to flow from the first hydraulic port to the tankgalley, the spool closes the first spool passage between the power coreand the first hydraulic port associated with the spool, and the spoolcloses the fourth spool passage between the tank galley and the secondhydraulic port associated with the spool; (9) wherein when activation ofone or more of the spools of one or more of the fixed/variable valvesoccurs in a manner causing said one or more of the of the activatedspools to be in the first non-neutral position, each of the spools soactivated causes a partial restriction in the fifth spool passage ofeach of the activated spools in the first non-neutral position and inthe open center core passing therethrough, (A) causing the hydraulicfluid pumped at a constant rate by the fixed displacement pump throughthe open center core to increase in pressure between the fixeddisplacement pump and the one or more restrictions caused by each ofsaid activated spools that are in the first non-neutral position, (B)wherein the variable displacement piston pump pumps hydraulic fluid atan increased rate to the power core of each of the fixed variablevalves, increasing the hydraulic fluid flow and hydraulic fluid pressurein the power core, and (C) wherein each of the activated spools in thefirst non-neutral position permits hydraulic fluid in the power corehaving increased pressure to flow through the open first spool passageto the first hydraulic port associated with each activated spool in thefirst non-neutral position; and (10) wherein when activation of one ormore of the spools of one or more of the fixed/variable valves occurs ina manner causing said one or more of the activated spools to be in thesecond non-neutral position, each of the spools so activated causes apartial restriction in the fifth spool passage of each of the theactivated spools in the second non-neutral position and in the opencenter core passing therethrough, (A) causing the hydraulic fluid pumpedat a constant rate by the fixed displacement pump through the opencenter core to increase in pressure between the fixed displacement pumpand the one or more restrictions caused by each of said activated spoolsthat are in the second non-neutral position, (B) wherein the variabledisplacement piston pump pumps hydraulic fluid at an increased rate tothe power core of each of the fixed variable valves, increasing thehydraulic fluid flow and hydraulic fluid pressure in the power core, and(C) wherein each of the activated spools in the second non-neutralposition permits hydraulic fluid in the power core having increasedpressure to flow through the open second spool passage to the secondhydraulic port associated with each activated spool in the secondnon-neutral position.
 7. The fixed/variable hybrid system of claim 6wherein the open center/power core passage further comprises a checkvalve that permits hydraulic fluid to flow through the open center/powercore passage from the open center core to the power core when thehydraulic fluid pressure in the open center core exceeds the hydraulicfluid pressure in the power core.
 8. The fixed/variable hybrid system ofclaim 7 wherein the check valve prevents hydraulic fluid from flowingthrough the open center/power core passage from the power core to theopen center core when the hydraulic fluid pressure in the power coreexceeds the hydraulic fluid pressure in the power core.
 9. Thefixed/variable hybrid hydraulic system of claim 8 further comprising:(1) a load sense signal port associated with the variable displacementpiston pump, wherein an increase in hydraulic fluid pressure received bythe load sense signal port cause the variable displacement piston pumpto pump hydraulic fluid at an increased rate, and wherein a decrease inhydraulic fluid pressure received by the load sense signal port causesthe variable displacement pump to pump hydraulic fluid at a decreasedrate; (2) a sense signal passage hydraulically connecting the opencenter core and the load sense signal port, wherein the hydraulicconnection between the sense signal passage and the open center core islocated between the fixed displacement pump and the first spool of thefirst fixed/variable valve downstream of the fixed displacement pump inthe open center core; (3) wherein when activation of one or more of thespools of one or more of the fixed/variable valves occurs in a mannercausing one or more of the activated spools to be in either a firstnon-neutral position, or a second non-neutral position, increasedhydraulic fluid pressure in the open center core is hydraulicallycommunicated through the sense signal passage to the load sense signalport.
 10. The fixed/variable hybrid system of claim 6 wherein themaximum pump output of the fixed displacement pump is less than themaximum pump output of the variable displacement piston pump.
 11. Thefixed/variable hybrid hydraulic system of claim 6 wherein each of thespools in each of the fixed/variable valves has associated therewith aspool activator, wherein each of said spool activators is capable ofcausing movement of the spool associated therewith to either a neutralposition, a first non-neutral position, or a second non-neutralposition.
 12. The fixed/variable hybrid hydraulic system of claim 10wherein each of the spools in each of the fixed/variable valves hasassociated therewith a spool activator, wherein each of said spoolactivators is capable of causing movement of the spool associatedtherewith to either a neutral position, a first non-neutral position, ora second non-neutral position.